Rare Dermatology News

Disease Profile

Fetal methylmercury syndrome

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Methyl mercury antenatal exposure; Minamata disease


Congenital and Genetic Diseases; Ear, Nose, and Throat Diseases; Mouth Diseases


The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.

Orpha Number: 1917

A rare disorder characterized by a group of symptoms that may be observed in a foetus or newborn when the mother was exposed during pregnancy to excessive amounts of methylmercury.

Accidents have led to the birth of about 800 affected children worldwide over the last 50 years.

Clinical description
In the late-1950s, methylmercury toxicity became highly publicised after an outbreak of cerebral palsy and microcephaly in newborns from the fishing village of Minimata Bay, Japan. These abnormalities were caused by methylmercury contamination of fish in the bay, and were termed Minimata Disease. Similar intoxications also occurred in Iraq after seeds contaminated with methylmercury were mistakenly used to make bread. In this population, infants exposed in utero displayed psychomotor retardation and cerebral palsy. Similar neurological impairment has been reported in other instances of food contamination, such as in infants of American Indian women who ingested pork contaminated with phenylmercuric acetate.

There are two main types of mercury, metallic mercury (a heavy liquid element at room temperature, used in thermometers) and organic mercury (like methylmercury, used as antifungal agent in seed dressings). The selective neurotoxicity of organic mercury does not appear to apply to metallic mercury and its salts. Methylmercury is lipophilic and more readily distributed to the brain tissue than mercuric salts. Metallic mercury does not cross the placenta readily, and it has been estimated that the rate of methylmercury transport into the brain may exceed that of mercury by a factor of 10.

Diagnostic methods
Exposure to methylmercury can be monitored by measuring the concentration in the hair. All fish contain some methylmercury, and frequent consumption of highly contaminated fish can lead to a hair concentration of methylmercury ranging between 10 and 50 ppm. A level of 50 ppm in hair has been established as the lowest toxic level, and the World Health Organization (WHO) has applied a safety factor of 10 to cover risks in the most sensitive populations. Thus, 5 ppm has been generally adopted as the international standard for the upper tolerable level of mercury in hair.

Management and treatment
Since maternal exposure to methylmercury is primarily through fish consumption, it is recommended that women of childbearing age should not consume more than 350g of fish per week. In addition, they should not be occupationally exposed to air concentrations of mercury vapor greater than 0.01 mg. per cubic meter, to inorganic and phenylmercuric compounds at concentrations greater than 0.02 mg per cubic meter, or to any detectable concentration of methylmercury.

Visit the Orphanet disease page for more resources.


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Hearing impairment
Hearing defect

[ more ]

Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference

[ more ]

Muscular hypotonia
Low or weak muscle tone
Short stature
Decreased body height
Small stature

[ more ]

Visual impairment
Impaired vision
Loss of eyesight
Poor vision

[ more ]


Learn more

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

In-Depth Information

  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.